y. feng

To enhance the firefighting capabilities of traditional dry powder extinguishers, we incorporated an air-assisted supersonic nozzle, which is simulated using Euler-Lagrange interphase coupling to simulate the injection of firefighting agents into a supersonic, two-dimensional axisymmetric gas flow from a bypass injector. During the simulation, we employed our newly developed modified drag coefficient model, capable of accommodating a broad spectrum of particle Reynolds and Mach number conditions. Parameter studies show that an increase in the injector position, angle, and total pressure ratio generally causes a decrease in the average particle velocity vp,a, and an increase in the dispersion Ψp and velocity unevenness Φvp; an increase in the total pressure ratio of the main nozzle leads to an increase in Φvp and vp,a. However, under specific conditions, the monotonic dependency upon these parameters may be disrupted. For example, the performance indicators at the position of the injector near the nozzle throat and a larger total injector pressure ratio, as well as vp,a at smaller injection angles and Ψp at larger injection angles, may run counter to the monotonicity.

In order to study the unsteady flow and vortex characteristics of tongue cavitation, numerical calculation is carried out for the whole flow channel given different conditions. Then, the calculation results are verified experimentally. The results show that after the occurrence of tongue cavitation in the centrifugal pump, it deteriorates with the decrease of NPSHa. However, when NPSHa is reduced to 3.78 m, it does not change significantly anymore with the decrease of NPSHa. The extrusion of fluid by the vapor at the tongue promotes the formation of the separation vortex, and the re-jet flow caused by the separation vortex leads to vapor shedding. The frequency of cavitation shedding is consistent with the frequency of vortex shedding. In the vorticity transport equation, the relative vortex stretching term and the relative vortex dilatation term dominate the vapor shedding by controlling the change in vorticity. The baroclinic torque term mainly affects the change of vorticity at the vapor-liquid interface, but to a much lesser extent than the first two terms.